Pete Wedderburn

Pete Wedderburn qualified as a vet twenty-five years ago, and now spends half his working life writing newspaper columns. He lives in Ireland with his wife, two daughters and a menagerie of dogs, cats, poultry and other furry and feathered companions. Pete answers readers' queries about their pets' health in his video Q&A – he is also on Twitter as @petethevet and has a Facebook Fan Page.

Why the US polo ponies would not have died in the UK

I've been following the shocking story from Florida, where twenty one polo ponies died last weekend at the start of the US Open competition. To quote from a local veterinarian's blog, "one by one, the horses belonging to one team staggered, fell and died–in front of the 4,000 fans assembled for this SuperBowl of polo. Tarps were set up to shield the horses' death throes from the onlookers as veterinarians rushed to place IV catheters and administer medications in an attempt to reverse the symptoms. To no avail. Every single affected horse died."

At the time, exposure to some toxin was strongly suspected: five horses in the group remained completely unaffected. It can't have taken much detective work to find out the origin of the toxin: the healthy horses were the only ones that had not received a vitamin and mineral injection. News reports now state that a local pharmacist made up a prescription based on a request from a veterinarian, and the pharmacy has admitted that "the strength of an ingredient in the medication was incorrect."The precise identity of the toxic ingredient has yet to be specified, but it's irrelevant. Somebody made a simple mistake: perhaps a decimal point was wrong, or perhaps the wrong bottle was picked up, and the "tonic" ended up being as lethal as a bullet in the head.

Of course the incident was a deeply unfortunate accident, and it's raised many questions: should it be permissible for pre-event injections be given to the horses to enhance their performance? Should only specified substances be banned?

It's interesting that the series of events could not have happened in the UK for a simple reason: we don't have the "compounding pharmacies" that are common-place in the USA. These pharmacies allow veterinarians to create made-to-order medications out of any list of active ingredients that they select. There's no tradition for this type of prescribing in the UK, and vets are restricted to using products that are already on the market.

There are very tight regulations governing drugs used by vets in the UK and throughout Europe. Vets are primarily obligated to use products licensed only for the species under treatment – this is the safest route, because the drugs have been tested and approved for their purpose. Dog wormers must be given to dogs; cat wormers to cats.

If an appropriate medication is not available (e.g. for rare diseases or for minority species where there's no licensed product), vets are allowed to use medications licensed for other species (e.g. a cattle dewormer, Ivermectin, has been used over the years to treat parasites in small animals such as guinea pigs).

If the only formulation of a drug that's available is licensed only for humans, not animals, then again it can be used, but strict guidelines must be followed. Examples include chemotherapy drugs used to treat animals with cancer.

The use of drugs in these different ways is controlled by vets being obligated to follow a tiered flow-chart of decision-making known as the "Cascade". If vets prescribe drugs without following the Cascade (e.g. if they use a human drug when there's a perfectly acceptable animal drug), then they risk prosecution.

On the occasions that an unlicensed drug is used, the animal's owner has to be informed that there may be unknown and unpredictable side effects, because the drug has not been fully evaluated in the species for which it's being used.

There are two reasons for the rules. Firstly, they prioritise the safety of the animals being treated. And secondly, they protect manufacturers who've spent money having products licensed for animal use from being undercut by cheaper, untested drugs.

These regulations can be onerous and awkward for vets, and they can add to the cost of treatment for owners (e.g. cheap generic drugs that are only licensed for humans cannot be used). But when you hear about incidents like the polo ponies in Florida, you begin to understand why it can make sense to have tight regulation of veterinary medicines.